ANDROID: GKI: export saved_command_line

Some driver modules require the ability to parse the kernel command
line outside the <modulename>.parm=<val> set on Android.  For example
androidboot.console=.  Past attempts ('03) to upstream and export
this key piece of content has come under resistance because
preference has been to support the existing api __setup(str,func),
which is only available to built-in, and push modules towards only
using the documented kernel parameter interface cited above or to
Device Tree and not react to any other out-of-band content.

Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Test: compile
Bug: 142496416
Change-Id: Ia349dce6f7e467b40b9fd95e40f52ea9a8f7e51d